Impedance matching circuit for a multi-band radio frequency device

ABSTRACT

In an impedance matching circuit for a multi-band radio frequency device, a first radio frequency signal in a first sub-band of a multi-band radio frequency signal is selectively outputted. Further, a second radio frequency signal in a second sub-band of the multi-band radio frequency signal is selectively outputted. Selective outputting is done through partly shared and partly non-shared reactive elements, without the need to switch reactive elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impedance matching circuit for amulti-band radio frequency device, and further to such multi-band radiofrequency device, and an impedance matching method.

More particularly, such impedance matching is done at sub-bands of amulti-band radio frequency signal in order to match impedances betweenvarious parts of the multi-band radio device such as between amplifierstages, between mixers and amplifier stages, or the like.

2. Description of the Related Art

U.S. Pat. No. US 6,243,566 discloses impedance matching for a poweramplifier in a dual band transmitter for a radiotelephone. For example,such a dual band transmitter radiotelephone can use the GSM system whichoperates at 900 MHz, and the DCS system, which is similar to GSM exceptthat it operates at 1800 Mhz. In a two-stage power amplifier, aninter-stage matching circuit matches the impedances between a firststage and a second stage of the two-stage power amplifier. Theinter-stage matching circuit optimizes the impedances at 900 Mhz or 1800MHz depending on which transmission mode is in use. Two field effecttransistors are used as power amplifier stages. Between the stages is a15 pF capacitance, and at the source of the first stage is a small 3 nHinductance which is connected to a voltage source. A 2.7 pF capacitanceis connected between the inductance and the voltage source. A 100 pFcapacitance is also connected to the voltage source with a diodeconnected from the 1000 pF capacitance to ground. A 1.5 kΩ resistor withan input node is connected between the 1000 pF capacitor and the diode.When a voltage source is connected to the input node, the diode turns onand the 1000 pF capacitance dominates the impedance of the interstagematching circuit. The capacitance values are calculated so that 900 GSMsignals from the first stage of the power amplifier are matched to thesecond stage when the input node is connected to a 2.7 V positivevoltage source. When a zero, negative, or floating voltage source isconnected to the input node, the 2.7 pF capacitance is connected to theinput node, and the 2.7 pF capacitance and the 3 nH inductance dominatethe impedance of the inter-stage matching circuit which matches the 1800MHz signals to the second stage. Thus, a voltage applied to an inputnode, and a diode switch determine a GSM mode or DCS mode of theimpedance matching circuit. The impedance matching network, is thusshared for receiving GSM of DCS sub-band signals.

Other systems used with multi-band radio frequency devices includeNMT-450 operating at 450 MHz, AMPS and D-AMPS operating at 800 MHz, PCSoperating at 1900 MHz, or still other systems.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an impedance matchingcircuit for a multi-band radio frequency device with reduced complexityand no need for external mode control of the impedance matching circuititself.

It is another object of the invention to provide such an impedancematching circuit that avoids use of switches in a signal path.

In accordance with the invention, an impedance matching circuit for amulti-band radio frequency device is provided, the impedance matchingcircuit comprising:

a frequency selective network comprising a first frequency selectivesub-network that is configured to selectively output a first radiofrequency signal comprised in a first sub-band of said multi-band radiofrequency signal, and a second frequency selective sub-network that isconfigured to selectively output a second radio frequency signalcomprised in a second sub-band of said multi-band radio frequencysignal, said first and second frequency selective sub-networks beingswitch-less networks.

The invention is based on the recognition that frequency selection ofsub-bands using partly shared frequency selective sub-networks renderswitches obsolete. The invention is further based on the recognitionthat, when implementing impedance matching networks as an integratedcircuit use of switches in series or parallel to a capacitor or inductormay cause the circuit not to work under all circumstances, depending onthe parasitics associated with the switches and switched components.This is because a switch in IC form has a large resistance whichdegrades the performance of the inductor or resistor being switched,particularly at very high frequencies.

In an embodiment of an impedance matching network according to theinvention, one sub-network is formed of a common inductor coupled to aninput node of the impedance network and a reference potential such asground, and, for dual band operation, a capacitor in a seriesarrangement of two capacitors, and another sub-network is formed of thecommon or shared inductor, and another capacitor of the seriesarrangement. In that embodiment, the one capacitor is connected betweenthe input node and an output node for the lower sub-band, and the othercapacitor is connected to that output node and a further output node forthe higher sub-band. Herewith, a very simple network is obtained thatautomatically passes sub-bands to the two output nodes. Because there isonly one inductor rather than two, had two separate impedance networksbeen used, also chip area is saved. By selectively switching on/offamplifiers for various sub-bands that are coupled to the impedancematching network, when implemented in a transmitter only the desiredsub-band is transmitted. This embodiment may very easily be extended tomulti-band operation including more than two sub-bands. For example, forthree band operation, simply a capacitor is added to the seriesarrangement thus creating a third output node.

The impedance matching network may be implemented to accommodatedifferential or single-ended circuit elements such as amplifier stages,mixers, or any other circuit element where impedance matching formulti-band operation is needed.

In another embodiment of an impedance matching network according to theinvention, capacitors for sub-band selection are provided that arecoupled to successive nodes of a series arrangement of inductors.However, in this parallel-capacitor implementation, more inductors areneeded than in the above series-capacitor implementation.

In an embodiment of the invention, the impedance matching network isincluded in a transmitter path a multi-band radio frequency device, andis arranged between mixer(s) and controllable amplifiers for differentsub-bands.

In another or further embodiment of the invention, the impedancematching network is included in a transmitter path a multi-band radiofrequency device, and is arranged between common pre-amplifier stagesand controllable non-sub-band-shared amplifiers stages for differentsub-bands.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of a multi-band radio device according to theinvention.

FIG. 2 shows a first embodiment of an impedance matching circuitaccording to the invention, coupled to a pair of quadrature mixers, fordual band operation.

FIG. 3 shows an embodiment of an impedance matching network according tothe invention, for three-band operation.

FIG. 4 shows another embodiment of an impedance matching networkaccording to the invention.

FIG. 5 shows an embodiment of an impedance matching circuit according tothe invention, coupled between common pre-amplifier stages and separateamplifiers for sub-bands, for dual band operation.

Throughout the figures the same reference numerals are used for the samefeatures.

DESCRIPTION OF THE DETAILED EMBODIMENTS

FIG. 1 is a block diagram of a multi-band radio device 1 according tothe invention. In the embodiment shown, signals are differential andquadrature. In other embodiments, signals may be single-ended and/ornon-quadrature. Shown in detail is a transmitter part of radio device 1with a pair of quadrature IF mixers 2 and 3, coupled to a signal adder4. IF-mixers 2 and 3 mix base band signals I_IN and Q_IN with 0° and 90°phase shifted oscillator signals provided by an oscillator 5 via a phaseshifter 6. At output side, signal adder 4 is coupled to an IF amplifier7 that provides an amplified IF signal to IF phase shifter 8. IF phaseshifter 8 provides differential quadrature signals to a pair of RFmixers 9 and 10 that otherwise receive phase shifted oscillator signalsfrom an oscillator 11 via phase shifter 12. A signal adder 13 addsquadrature mixed RF signals. Further shown are controllable amplifiers14 and 15 for a higher sub-band of the multi-band, in the example givendual band, and controllable amplifiers 16 and 17 for the lower sub-bandof the multi-band, so-called PCS and CELL bands. In the example giventhere are two controllable amplifiers per sub-band. This is because, intransmitters, sub-bands such as PCS usually are split into two furthersub-bands. Selectivity of these further sub-bands is achieved moreupstream in the transmitter, by separate band pass filters (not shown indetail here). Because these further sub-bands are close to each other infrequency, there is no need to build in selection thereof in theimpedance matching circuits of the invention as shown in detail in FIGS.2-5. For selection of the PCS sub-band, amplifiers 14 and 15 areswitched on and amplifiers 16 and 17 are switched off. For selection ofthe CELL sub-band, amplifiers 16 and 17 are switched on and amplifiers14 and 15 are switched off.

FIG. 2 shows a first embodiment of an impedance matching circuit 20according to the invention, coupled to quadrature mixers 9 and 10, fordual band operation. Signal adder 13 is implemented by connectingrespective differential outputs of mixers 9 and 10 in common input nodes21 and 22. Impedance matching network 20 comprises inductors 23 and 24respectively being coupled between nodes 21 and 22 and ground, a seriesarrangement of capacitors 25 and 26 coupled to input node 21, and aseries arrangement of capacitors 27 and 28 coupled to input node 22.Series arrangements of capacitors 25 and 26, and of capacitors 27 and28, have output nodes 29 and 30 for the CELL band, and output nodes 31and 32 for the PCS band. Capacitors 25 and 26, and 27 and 28, aredimensioned such that for the higher frequency PCS sub-band, RF signalflow effectively and substantially is via signal paths formed bycapacitors 25 and 26, and 27 and 28, the other signal paths viacapacitors 25 and 27 alone effectively being short-circuits, and thatfor the lower CELL sub-band, RF signal flow effectively andsubstantially is via signal paths formed by capacitors 25 and 27 alone.As compared to prior art solutions that use separate and non-sharedmatching circuits for dual-band, at least two mixers, an RF phaseshifter are saved.

FIG. 3 shows an embodiment of an impedance matching network 40 accordingto the invention, for three-band operation. In addition to inductors 23and 24, and capacitors 25, 26, 27, and 28, for three sub-band operation,impedance matching circuit 40 has capacitors 41 and 42. Herewith,differential output signals 43, 4, and 45 for three sub-bands areobtained.

FIG. 4 shows another embodiment of an impedance matching network 50according to the invention. Impedance matching network 50 has a seriesarrangement of inductors 51, 52, and 53 between input node 21 andground, and a series arrangement of inductors 54, 55, and 56 betweeninput node 22 and ground. For sub-band selection of three sub-bands,capacitors 57 and 58, capacitors 59 and 60, and capacitors 61 and 62 areprovided. Capacitors 57 and 58 select the highest sub-band, capacitors59 and 60 select the mid sub-band, and capacitors 61 and 62 select thelowest sub-band.

FIG. 5 shows an embodiment of an impedance matching circuit 70 accordingto the invention, coupled between common pre-amplifier stages 71, 72,and 73, and separate amplifiers 74 and 75 for sub-bands, for dual bandoperation. Impedance matching circuit 70 has the same structure asimpedance matching circuit 20, and comprises inductors 76 and 77, andcapacitors 78, 79, 80, and 81. With one of the amplifiers 74 and 75switched on at a time, the other one of amplifiers 74 and 75 is switchedoff.

In view of the foregoing it will be evident to a person skilled in theart that various modifications may be made within the spirit and thescope of the invention as hereinafter defined by the appended claims andthat the invention is thus not limited to the examples provided. Theword “comprising” does not exclude the presence of other elements orsteps than those listed in a claim.

1-18. (canceled)
 19. An impedance matching method for a multi-band radiofrequency device, said impedance matching method comprising: selectivelyoutputting a first radio frequency signal comprised in a first sub-bandof a multi-band radio frequency signal; selectively outputting a secondradio frequency signal comprised in a second sub-band of said multi-bandradio frequency signal, said first and second selectively outputtingbeing done without applying switching in a signal path.
 20. An impedancematching method as claimed in claim 19, further comprising selectivelyoutputting a third radio frequency signal comprised in a third sub-bandof a multi-band radio frequency signal, said third selectivelyoutputting being done without applying switching in the signal path.